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I'm currently making 9 litres of quite thick lentil soup in a 10 litre stainless steel stockpot. It needs to simmer gently for an hour or two. Despite the sandwich base and my weakest gas ring on minimum*, it needs stirring every few minutes or it will stick, and soon burn.

I've found this with other similar soups too (e.g. split pea and ginger) and dal. What they have in common is that they're too thick to convect properly. Today's is worse because I'm making it extra thick thicker for further dilution to serve about 40 people. Small batches can be done n my 3.5 litre slow cooker, though even in that it can stick.

Because this cooks for quite a long time, I need to be able to get on with other things, not all in the kitchen. So I wondered about solutions for automated stirring. In small vessels in the lab, for example, there are magnetic stirrers built in to hotplates. Is there something larger for use at home, whether a product (perhaps something that could be repurposed), a DIY design, or something I haven't considered.

* I have a flame diffuser, but it's a bit small for the pan and couldn't be trusted to take the weight. A diffuser that clipped under the pan supports would be interesting, like the wire gauze sometimes used with bunsen burners.

Chris H
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  • I tried the flame diffuser wedged between the burner and pot support, but it's too big to fit centrally and after a few minutes the wooden handle started to scorch where it touched the metal. – Chris H Apr 07 '22 at 12:53
  • Someone should come up with some sort of immersion circulator for thick liquids... – Luciano Apr 07 '22 at 14:15
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    You could probably rig a paint stirrer, clamp-stand and electric drill. Trick would be to get the drill going slow enough to stir without creating a soup tornado. – bob1 Apr 07 '22 at 22:47
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    I have fantasized about using a magnetic lab stirrer in the kitchen for most of my adult life. – Tom Apr 08 '22 at 01:28
  • Not quite the answer, so I won't post it as such, but I regularly cook (very) thick soups, at least on the level of Dal soups, and have zero issues with burning in. I usually let them simmer for 20-30 minutes with no attention of mine at all. This is in stainless steel pots (I cannot exactly tell you what material or coating they have - if there is any, it's not visible and does not go away after decades of use, so I assume it's just stainless) on an induction stove. Maybe add the material/type of your pot, maybe that helps people come up with even better answers. – AnoE Apr 08 '22 at 10:31
  • @AnoE it was only after the best part of an hour that the sticking got bad, but induction might help as it heats the pan base quite evenly on low power, while minimum gas heat tends to be concentrated in the middle. While I said "sandwich base" and "stock pot", implying stainless, you're right that I didn't explicitly state the surface – Chris H Apr 08 '22 at 11:52
  • Hah, my non-native language skills forsake me for these terms, @ChrisH. ;) – AnoE Apr 08 '22 at 12:30
  • https://www.lakeland.co.uk/62575/Lakeland-Cordless-Automatic-Pot-Stirrer-for-14cm-to-24cm-Pans – Richard Apr 08 '22 at 18:01
  • They do make magnetic stirrers for home cooking use, though they generally take the form of a single standalone burner, not something built into a regular cooktop. Note that these would only work with a ceramic or glassware pot. A typical steel or cast-iron one would not work, since the magnetic field will be shielded by ferrous metal. – Darrel Hoffman Apr 08 '22 at 20:49
  • @DarrelHoffman Interesting. I suspect they'd work best with aluminium pans, like the large catering pans, unless there's something clever about the heat source to allow it to work under glass or ceramic (I can see a use for custards in a double boiler setup) – Chris H Apr 08 '22 at 20:55
  • Aluminum *might* work? I'm trying to remember my physics to think if non-ferrous metal still has that effect of shielding magnetic fields. I don't think there's anything special about the heat source that works best under glass or ceramic, it's just that ferrous metal (which is the vast majority of cookware - hence why magnetic stirrers maybe didn't catch on much outside of the lab - where everything is glass usually) definitely won't work, and I'm not sure about other metal. – Darrel Hoffman Apr 08 '22 at 21:09
  • @DarrelHoffman Al would work nicely. I happen to have some strong magnets, aluminium plate, and a sewing needle right here so could mock it up! – Chris H Apr 09 '22 at 06:58

4 Answers4

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When I am cooking very thick soups I often put the pot in the oven instead of the stove and cook it that way. Because the heat is distributed around the entire surface I don't run into problems of it burning and sticking. Be sure to manage the temperature though, just around boiling is good.

GdD
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    I thought about that, but was sure this pot didn't fit. Prompted by your answer, I had another check. It just fits if I put the shelf on the floor of the oven instead of where it's supposed to go – Chris H Apr 07 '22 at 12:42
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    There's nothing wrong with that as long as the pot is rated for the oven temperature. You don't want it resting directly on the oven floor, but having the grate in between should be fine. – GdD Apr 07 '22 at 12:44
  • I don't honestly know about the handles (it's a cheap ikea one) but as I can set 100--110°C for the oven and put the pan in hot they should be fine as handles can get that hot on the hob. – Chris H Apr 07 '22 at 12:48
  • Yeah, that's a safe assumption. – GdD Apr 07 '22 at 12:53
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    That turned out to be the solution I really needed. I might cook in metric but I now have 2 imperial gallons of slightly concentrated soup cooling in the fridge to fuel a bunch of hungry cyclists on Saturday (and I've just worked out that apparently fuelled by hearty soup a cyclist gets about 54 miles per gallon) – Chris H Apr 07 '22 at 16:50
  • I'm glad to hear it works for you, and I hope your cycling friends enjoy the result. If you're happy why don't you accept this answer? – GdD Apr 08 '22 at 08:17
  • I was torn between accepting the one that solved my problem, and the one that answered my question as written. But more to the point I tend not to accept answers for about 24 hours to give everyone a fair chance to respond without being discourages – Chris H Apr 08 '22 at 11:48
  • A sensible policy @ChrisH. If this recipe is good I wouldn't mind getting it, I'm in the market for a good lentil soup recipe. Maybe ping it in chat? – GdD Apr 08 '22 at 12:59
  • Let us [continue this discussion in chat](https://chat.stackexchange.com/rooms/135421/discussion-between-chris-h-and-gdd). – Chris H Apr 08 '22 at 20:32
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I thought we had a question about this some time ago, but I can't locate it. Google or Amazon search "auto stirrer for kitchen." Here is one example. Plug it in. It stirs for you. Not sure how thick is too thick for these, so maybe someone with personal experience can comment.

Given the discussion, I will just point out that there are other designs.

moscafj
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  • Having seen a video it appears to work by stick-slipping against the base of the pan, and vibrating its way round. So I suspect it's not going to work in my case. Also the legs are far too short - the battery case would barely stick out of my soup, and "Never leave device unattended" rather defeats the object. But it's good to know that things exist – Chris H Apr 07 '22 at 12:46
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    The never leave it unattended sounds like a legal protection thing to me, if you leave your pot unattended and your house burns down you can't point the finger at them. – GdD Apr 07 '22 at 12:52
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    I used to have a device of this type. As far as I can remember, it did work - not perfectly, but it was good for things like puddings thickened with egg yolk or starch, it prevented that thick overcooked or burned layer on the bottom. It is too small though, because only the legs are allowed to be immersed in liquid, the whole case has to be above. Also, mine broke down even though it hadn't been used too much, and I didn't feel like it added enough value to be replaced. – rumtscho Apr 07 '22 at 12:57
  • @GdD I'm sure you're right, but the [Lakeland one](https://www.lakeland.co.uk/62575/Lakeland-Cordless-Automatic-Pot-Stirrer-for-14cm-to-24cm-Pans#product-details-accordion) doesn't say that in the manual (and has a few other advantages like being rechargeable, and bracing against the pan, but doesn't go quite deep enough for my use). That I think is sold under the SAKI brand in other countries. In fact the sales pitch includes "while you're laying the table" so it's explicitly sold to be left unattended (but only 2 hours runtime) – Chris H Apr 07 '22 at 12:57
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    @rumtscho a big red flag to me is that while it's clearly only immersible up to the top of the legs, that crucial dimension isn't specified . Even if the product is fit for purpose, the marketing isn't. – Chris H Apr 07 '22 at 13:03
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    This design might work better for thicker soups, as it can be adjusted to get into the corner and scrape the bottom of a large range of pot sizes: https://smile.amazon.com/StirMATE-Automatic-Variable-Self-Adjusting-Powerful/dp/B076HH4WZM – Joe Apr 07 '22 at 14:47
  • @Joe when searching for more info on the example in this answer I found that StirMate had the best reviews. It also fits the biggest pans of any I can find. Would be worth a look if I make a habit of it - I might even be buying a bigger pan if I can find anywhere to store it – Chris H Apr 07 '22 at 14:59
  • Dang! Not I gotta buy one of those machines...that I knew nothing about 10 minutes ago! – gnicko Apr 14 '22 at 23:44
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If you're after DIY and don't mind some dilution, then Direct Steam Injection (DSI) might be your answer. In a domestic environment you could get your steam from the top of a pressure cooker using a hose and your soup pot could be insulated. The bubbles of steam both transfer heat and, rising, stir your soup.
DSI is a used in industrial scale food processing, as evidenced by this university course although generally in a continuous process (in pipes).

Ken Mercer
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There are also products on the market named "soup makers" which has as one of it's features: no need to stir

E.g. https://www.philips.nl/c-m-ho/koken/soupmaker-topic

enter image description here

This picture from a different one shows the stirring part

enter image description here

Thomas
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    The asker is trying to work with large batches (9 liters in a 10 liter pot), which is part of the problem they are trying to solve. Not sure a 1.2 liter device would help much? – Stephie Apr 08 '22 at 09:16